1. Field of the Invention
This invention relates to interferometers and especially to a heterodyne, phase-measuring interferometer (HPMI).
2. Description of the Prior Art
Phase uniformity of a laser beam across a flat plane which is transverse to its propagation direction or axis is important because it is difficult to focus beams which have a non-uniform transverse phase profile. Apparatus commonly used for phase analysis of a wavefront requires a lateral or shear interferometer to convert slope data into phase data or a superheterodyne technique which compares the phase of a local oscillator (laser) to the test beam wavefront. The first apparatus requires complicated and time-consuming solutions of simultaneous equations or an analog network of resistors to obtain phase data from the slope data. The second apparatus requires the phase-locking of two lasers which is very difficult to accomplish, especially in non-laboratory conditions.